The Spinal Cord: Review - Ends at L2 because the growth of the neuro system Is slower than the vertebral column o Spinal nerves continue to exit cauda equina - Spinal cord is not uniform in length, enlargements in Cervical & Lumbosacral regions o Enlargements are due to presence of limbs (brachial plexus coming from C5-T1, and lumbosacral plexus from L1-S4 Slide 2: Neuroepithelium develops a segmental organization develops into neurons & glial cells o Segmental organization runs from cephalic region coccyx Slide 3: - The lumen of the neural tube becomes the central canal of the cord, and ventricles of the CNS filled with CSF o Ventricular system springs from central canal, which is filled with CNS - Syringomyelia o Enlarged central canal Central canal can develop a cyst or syrinx (fluid filled cavity) o As canal gets large, it puts pressure on axons that may be next to enlargement. Slide 7-9 - Notochord serves as primitive spinal column - Presence of notochord induces ectoderm to form the neural tube - This then induces the lateral mesoderm development into somites which give rise to sclerotome (vertebrae), myotome (muscles), dermatome (skin) Slide 10-13: - At each vertebral level, each segment of the neural tube innervates the dermatome/myotome of the somite associated with it - Because somites have segmental organization, spinal cord also has segmental organization - Dorsal ½ of spinal cord sensory - Ventral ½ of spinal cord motor o Innervation of muscles have a segmental organization: Flexing the hip: L2, L3 Extending the knee: L3, L4 Extending the ankle: L4, L5 - Sensory innervation of the skin is segmented into dermatomes Slide 14: Adult Spinal Cord - Central canal: runs length of the spinal cord, filled with CSF, size can enlarge and put pressure on grey matter and nerves associated - Grey matter: Neural epithelium (lots of cells) - White matter: axons of the neural epithelium that are myelinated - Ventral horn motor neurons - Dorsal horn sensory neurons Slide 15: Thoracic Spinal Cord - Distinguishing feature of thoracic spinal cord Presence of Lateral Horn found at T1-L2 - Reason for lateral horn: it gives rise to preganglionic sympathetic neurons that provide sympathetic innervation to the entire body - - Ventral White Commissure: Goes left right, o Associated with axons communicating b/w two sides of the spinal cord o If central canal gets larger, pressure will have greatest detriment to the white commissure Anterior ventral median fissure Posterior median sulcus (useful for distinguishing right vs. left of spinal cord) Posterior lateral sulcus (for distinguishing white matter of spinal cord into column of axons Anterior lateral sulcus where ventral roots exit Slide 16: Types of Neurons found in the spinal cord - Motor neurons o Innervating skeletal muscles or autonomic structures o Located primarily in ventral horn o Multipolar spinal motorneurons - Interneurons o They allow for elaboration of sensory signals and development of reflexes and complex circuits like walking, speech, movement o Functions- Important for turning on/off groups of neurons and processing post sensory neural information excitatory or inhibitory o Types: Intrasegmental interneurons (Renhsaw cell) The axons of these neurons stay within a single spinal cord area (e.g., an axon at T1 will not do anything outside of this local T1 area) Propriospinal interneurons Function – relaying information in a single spinal cord segment to other segments of spinal cords Short (3 segments, unilateral) o Does not cross limbs or body regions o Axons can span 2-3 spinal cord segments o Interconnect the motor neuron pools and connecting reflexes of uMN and LMN to work as a unit Intermediate o Helpful in coordinating the activity/movement of different limbs Long (entire length of cord, bilateral) o When we move, pair of spinal cord muscles will move as a unit (e.g, muscles in neck with muscles in the trunk) - Projection neurons o Sensory information making synpases in grey matter, and then information is relayed to higher level (brainstem, thalamus, cortex0 o Sending info from spinal cord high level Slide 18: (Testing for various interneurons) Intrasegmental interneuron Researcher dyed a single neuron to fill up and able to track it Long Long Propriospinal interneuron - Dissection of cats spinal cord Dye injected, taken up by neuron synapses and the dye is transported back, through retrograde transport, back to the cell body of the axon Black dots on both sides of the spinal cord, showing interneurons that are filled by the dye Presence of long axons connecting the movement of segments of upper & lower limb Short propriospinal interneurons - Gave electrical shocks in one segment of spinal cord and then measured this 2-3 segments below where they stimulated - Spikes in A show artificial stimulation, causing AP propagation in opposite direction, and a characteristic spike (antidromic spike) - As compared to regular synaptic activity spike that follows the first propagation - Stimulation in this backfiring manner activates interneurons in that area used to demonstrate, which tracing axons, them going from a place of stimulation to a place of recording and demonstrating the presence of short interneurons Slide 21: - Medial motor systems: control axial musculature – spinal muscles, muscles of the abdominal wall - Lateral motor systems: - In general, we see connecting the periaxial musculature are long propriospinal interneurons - Short propriospinal interneurons will connect lateral motor groups - Axons are running in a nucleus in an interphase along white matter, called the fasiculus propias Anatomy of the Gray Matter: Ventral Horn - Motor neurons that innervate a single muscle are clumped together in a single place, form motor nuclei o Different clumps innervate different muscles relative to other motor nuclei o In 3D, motor nuclei actually appear in columns , in cross-section motor nuclei appear circular or ovoid - Motor neurons located medially (recall medial motor systems) neurons innervating the paraxial or para spinal muscles are located more medially o As we move more laterally out, we find motor neurons that are more innervating the hand - Flexor/extensors are not mixed o Flexors more dorsally located o Extensors more ventrally located Cells within the grey matter are organized into 10 lamina Motor neurons are found in lamina IX (Medial vs. lateral) Lateral group appendicular musculature will be well developed particularly where brachial & lumbosacral plexus arise, which can be helpful for knowing where you are looking at along the spine A large lateral group you are likely where limbs are Lamina VII: - Intermediolateral cell column where motor neurons of sympathetic cells are found presence of these cells give us lateral expansion - Clarkes column part of spinal cerebella system dealing with proprioceptive information - Lamina VIII: Located more medially surrounding parts of medial IX Lots of polysynaptic reflexes Have many motor interneurons that are involved in reflexes Helps regulate gamma motor activity (contribute to setting sensitivity of motor spindle) Regulates resting tone all muscles have resting tension & conditions can occur where tone is too much (spasticity) or too is too little (waiters tip look due to imbalance of muscle tension) Anatomy of the Gray Matter: Dorsal Horn - - Dorsolateral zone of Lissauer: o Axons that are going b/w different segments, when dorsal root reaches dorsolateral zone, axons bifurcate (some axons go up, some go down), and thus are Information from this dorsal root is affecting several spinal cord segments Sensory pain afferents can ascend & descend to influence more than aa single segment of the spinal cord Marginal zone & substantia gelatinosa nocireceptor/pain information part of the spinal cord Nucleus proprius information from other modalities (vibration, touch, fine touch) NOT PAIN - DZ of Lissaeur has small diameter axons that come in & go to different spinal cord levels - entry zone for the dorsal root with mostly pain information ((small axons) coming into the lateral division - Pain fibers run through 3-4 spinal cord segments, influence activity of different spinal cord segments - important for identifying clinical manifestations of pain or loss of pain due to lesion, etc - Type 3 fibers, or Adelta fibers - Lamina 5 includes sensory integration of pain, vibration, proprioception - also Lamina 5, you will have projection neurons, which will project info to higher levels in the brain - C fibers are unmyelinated sensory axons (oldest fibers, slowest conduction of information, associated with visceral information as well) - lateral group of axons synapsing largely at lamina 1, 2 - axons come in and mostly go to the dorsal funiculus this is info that will ascend up the brain stem & eventually reach to cortex, telling us what’s going on with our skin in terms of fine touch, vibration, proprioceptors - type II fibers are second largest that will go to the middle part of dorsal horn with a lot of sensory information, interacting with lamina 3, 4, 5 - largest & fastest conductors carrying proprioception from muscle spindles & golgi tendon organs - part of lateral division of dorsal horn, where most axons are going straight up to the medulla/cortex - Axons also give off branches (collaterals) that target Lamina 9 - Monosynpatic input going from large A alpha axons to lamina 9 a knee jerk reflex uses such fibers (monosynaptic reflex) - Lamina 7 & 8 are also targeted, where we find motor interneurons that connect different motor neurons involving synaptic reflex activity axial section through dorsal roots reveal afferents of different diametes These are sensory axons, and we see axons with different sizes Nerve fibers are classified according to: diameter, degree of myelination, and speed of conduction Axons entering in the dorsal root divide into two divisions: according to axons diameters - medial fibers run most medially largest fibers (Type 1, Type II) - lateral division fibers that are smaller (Type 3, 4) Anatomy of the White Matter, Dorsal Horn - Like a nerve, white matter is composed of myelinated axons (cross section looks like a nerve) o Myelin from Oligodendrocytes, not Schwann cells o No CT in CNS, so not regrowth o Fiber tracts are bundled axons that have specific function (motor or sensory) - posterior dorsal roots come off here, located between the two sulcus - White matter is organized into ascending (sensory – blue) and descending (motor – red( 3 long tracts: lateral spinothalamic tract, dorsal columns, corticospinal tract (SUCK DIS COCK) Funiculi are associated with different and specific tracts 1. Spinothalamic tract in anterolateral funiculus carries pain & information & temperature & crude touch a. One of the oldest tracts in vertebrae system 2. Dorsal column carries information about fine touch & proprioception fast patheay 3. Corticospinal tract allows us to have voluntary movements a. Lateral tract in dorsolateral funiculus gives us voluntary control of fingers, hands, etc 4. Anterior part of corticospinal controls axial musculature Note: the amount of white matter decreases at lower levels of the cord…why? - - locating lateral horn presence or not (thoracic region) Cervical has a large lateral horn lateral motor groove sending out axons of the muscles of the limb and giving a large expansion o Also large amount of white matter o Axons for ascending & descending pathways Lumbar level o Lateral motor groove associated with this level, but we see more white matter bc white matter sensory tracts will be larger here o Descending motor tracts are coming into lumbar level and may be passing through to sacral - Sacral level o Expansion of ventral horn due to sacral spinal cord innervating lower limbs & need room those motor neurons o Not much white matter o We have: sensory & motor forming ascending and descending tracts Blood supply to the spinal cord - stroke involving anterior spinal artery will produce bilateral & deeply impacting symptoms - obstruction of posterior spinal artery will lead to a block of supply and will impact sensory information - vertebrae arteries run in the transverse cervical foramen - medullary arteries join the anterior & posterior spinal arteries, reinforcing blood supply to the arteries - Adamkiewicz is very large typically & comes off to the left at T10. Intervertebral foramen at T10 is typically much larger - the main anastomoses providing blood to lower part of spinal cord & corticospinal tracts occlusion of artery will lead to deprived blood from the lumbosacral enlargements in distal part of spinal cord paraplegia